1. Field of the Invention
The present invention relates to a PWM signal output circuit.
2. Description of the Related Art
Among motor drive circuits, there is a circuit configured to drive a motor based on a PWM (Pulse Width Modulation) signal (see, e.g., International Publication No. 2008/026319).
The motor drive circuit disclosed in International Publication No. 2008/026319 drives the motor based on the PWM signal with the duty cycle of 100%, for example, so that a voltage is applied to a motor coil of the motor for a long time, when starting a rotation of the motor. Then, when the rotation speed of the motor has increased to a certain extent, the motor drive circuit drives the motor based on the PWM signal with a duty cycle corresponding to a target rotation speed of the motor.
The motor drive circuit disclosed in International Publication No. 2008/026319 drives the motor based on the PWM signal with the duty cycle of 100%, for example, for a long time in order to rotate the motor reliably. Thus, at the time of starting the motor, a current flowing through the motor abruptly changes with the timing of phase switching, for example, and the noise when the motor rotates tends to become high. Further, the abrupt change in the current at the time of the phase switching deteriorates the torque efficiency as a result.